Spectral instruments are units for measuring absorbance/reflectance of a test sample by changing the intensity of light transmitted/reflected by the test sample, and are used in various fields. When a spectral instrument is applied to, for example, color measurement or blood tests, in the light transmitted through the test sample, absorbance is measured for a plurality of optic elements with different wavelengths, that is, for each wavelength of multi-wavelengths. As such an instrument, a rotor plate-type spectral instrument disclosed in Japanese Published Unexamined Patent Publication No. S59-131124 is available. This spectral instrument makes it possible to detect multi-wavelengths by mechanically rotating a rotor plate so that a filter that transmits an optic element of a wavelength to be detected is positioned in the light path.
However, the rotor plate-type spectral instrument selects a filter by mechanically rotating the rotor plate, so that it takes time to detect multi-wavelengths. Quick testing of many samples and many items is required in a blood test, however, the rotor plate-type instrument cannot meet this requirement.
As a unit to meet this requirement, for example, the half mirror-type spectral instruments disclosed in Japanese Published Unexamined Patent Publication No. H11-6766 and Japanese Published Unexamined Patent Publication No. S59-170734 are available. These spectral instruments are structured to detect multi-wavelengths by a plurality of half mirrors and a plurality of light receiving devices. The half mirror type spectral instrument divides incident light into transmitted light and reflected light by half mirrors, and uses the transmitted light as incident light on the half mirror positioned next, thereby detecting multi-wavelengths. Therefore, in comparison with the above-described rotor plate type spectral instrument that detects multi-wavelengths by mechanically selecting a wavelength, multi-wavelengths can be detected at high speed.